1. Field of the Invention
The present invention relates to a method of welding halogen-free thermoplastic foils or plates having intermediate layers, such as, for example, reinforcement layers placed between the thermoplastic foils. The method is carried out by means of a welding apparatus which includes a welding tool which can be heated to the desired welding temperature and a countertool which can be adjusted to a temperature which is below the melting temperature of the foils. The countertool has a profile which corresponds to the desired welding or stamping contour, particularly a cutting edge. The apparatus further includes a heat-conducting separating foil which can be placed in the welding apparatus and through which the thermal energy produced by the welding tool and required for plasticizing the thermoplastic foils is transmitted to the thermoplastic foils and from which the foils can be separated after the foils have been connected and after cooling.
2. Description of the Related Art
In a method of the above-described type known from German Patent 38 07 164, one of the two foils to be welded together, i.e., the lower foil, is pulled by means of a vacuum into a trough formed by one of the two tools of the welding press. In this manner, a bed for receiving and centering the layers, such as, e.g., reinforcement layers, is created. The lower foil has an edge portion which extends in a flat plane. Contacting this edge portion of the lower foil are the other foil, i.e., the upper foil, as well as the separating foil which is of high heat-resistant material, for example, polyimide, through which the major portion of the welding energy is supplied. As a result of this configuration, the welding seam is produced immediately on the separating foil even when reinforcement layers are provided. This is because the upper foil remains in contact with the separating foil, and the entire additional foil material required for sheathing the reinforcing layers must be obtained from the lower foil. This known method makes it possible to produce foldable objects, such as book covers, folding containers, and the like. However, this method does not make it possible to produce a welding seam approximately in the center plane of the reinforcement layers, as it is required, for example, in the manufacture of automobile sun visors.